Cheapest option - re-spring the front to your weight with non-progressive springs - Probably about $200 with servicing and all
Racetech does make a piston for it, which is the next cheapest option, you're probably looking close to $500 with springs, pistons, oil, etc.
GP Suspension makes 25mm carts, which will be about $1100-$1200 installed and setup for you.
Ohlins 30mm carts is next at around $1300-$1400 I think.
There are a few others out there, but these are the ones I know. All that said, if you are going fast enough to push the limits of the stock BPFs, then you're going to want to upgrade to the cartridges, because it's not the pistons which are causing all of the issues.
They are REALLY nice forks to begin with, so I would normally recommend to someone to just get them setup for your weight and skip the carts until you're ready to challenge the top level experts. That said, you can usually get really nice cartridge/shock combos for great prices, so I would save for that if I were you. The stock shock definitely needs replacing on the Gen 4 once you start pushing it out of the corners.
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